Indonesia issued the sixth tsunami warning on Thursday evening after a 6.8-magnitude aftershock rocked Bengkulu province in Sumatra Island, according to the Meteorology and Geophysics Agency.

Office workers wait at an open area outside their building in Jakarta's business district after tremors were felt from an earthquake. A massive 7.9-magnitude earthquake has struck off the west coast of Indonesia's Sumatra island, toppling buildings and briefly triggering a tsunami alert across the Indian Ocean region.

"The shock is potential for tsunami," said an official of the agency.

The powerful main shock with magnitude of 7.9 rocked Bengkulu province on Wednesday afternoon.

Until Thursday evening, powerful and moderate tremors frequently occurred in the area, according to the meteorology agency.

(Xinhua News Agency September 14, 2007